1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device in which an insulation film for causing the channel region of a MIS transistor to produce stress is provided on the channel region.
2. Description of the Related Art
Semiconductor devices, which include an Si element region, an element isolation region formed of an insulator and electrically isolating the element region from the other elements, and a metal insulator semiconductor filed effect transistor (MISFET) formed in the element region, are formed of, for example, a plurality of materials that can produce stress of different levels. Because of differences in stress level between the materials, stress occurs in the channel region just below the gate electrode of the MISFET.
In an n-type MISFET, it is known that, in general, when compressive stress occurs in the channel region, the mobility of electrons as carriers is reduced. Further, it is known that in a p-type MISFET, when tensile stress occurs in the channel region, the mobility of holes as carriers is reduced.
In light of the above, a stress film for causing the channel region of the n-type MISFET to produce tensile stress is provided on the n-type MISFET, thereby increasing the degree of mobility of electrons as carriers in the n-type MISFET, and hence enhancing the current driving capacity of the n-type MISFET. Similarly, a stress film for causing the channel region of the p-type MISFET to produce compressive stress is provided on the p-type MISFET, thereby increasing the degree of mobility of holes as carriers in the p-type MISFET, and hence enhancing the current driving capacity of the p-type MISFET.
When such stress films are employed, the stress that occurs in the channel region is influenced not only by the stress film provided on the gate electrode, but also by the stress films provided on the opposite sides of the gate electrode and the stress films provided on the source and drain regions. Accordingly, when a plurality of MISFETs are formed, the stress occurring in each channel region is strongly influenced by the layout of the gate electrodes around it.
The performance of the MISFET significantly depends upon the stress. Therefore, if the stress that occurs in the channel regions of MISFETs significantly differs in level, differences in characteristic between the MISFETs become great, which is not desirable in light of the operation, performance and/or power consumption of the semiconductor device.
Furthermore, a technique related to the above and aiming at enhancement of the mobility of MISFET carriers is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-60076.